This invention relates to a method for selectively hydrogenating ethylenically unsaturated polymeric materials.
Heretofore, several processes have been proposed for hydrogenating polymers containing ethylenic unsaturation. The polymers actually hydrogenated may contain only ethylenic unsaturation such as taught, for example, in U.S. Pat. No. 3,465,063 or the polymers may contain both ethylenic and aromatic unsaturation as taught, for example, in U.S. Pat. Nos. 3,113,986; 3,333,024; 3,595,942; 3,634,549; 3,644,588; 3,670,054; 3,700,633 and Re. 27,145. When the polymer subjected to hydrogenation contains both ethylenic and aromatic unsaturation, the hydrogenation may be accomplished such that a significant portion of both the ethylenic and aromatic unsaturation is converted as taught, for example, in U.S. Pat. Nos. 3,113,986; 3,595,942 and 3,700,633 or the hydrogenation may be completed selectively such that a significant portion of the ethylenic unsaturation is converted while little or no aromatic unsaturation is converted as taught, for example, in U.S. Pat. Nos. 3,634,549; 3,670;054 and Re. 27,145. The processes heretofore proposed are, or at least can be selective as between ethylenic (and acetylenic) unsaturation and aromatic unsaturation. The processes heretofore proposed, however, are not considered selective as between the various types of ethylenic unsaturation as indicated, for example, in U.S. Pat. No. 3,670,054 wherein it is indicated that isoprene segments are, generally, hydrogenated to approximately the same extent during hydrogenation as are butadiene segments.
While the hydrogenation processes heretofore proposed have, generally, been quite effective in producing polymeric materials having improved weatherability (ozone and oxygen resistance) and thermal stability, these processes, generally, cannot be operated so as to permit the retention of a controlled amount of ethylenic unsaturation, particularly in an elastomeric segment of a polymer even though the hydrogenation can be stopped and restarted as taught in U.S. Pat. No. 3,937,759. In fact, the hydrogenation processes heretofore proposed frequently result in substantially complete conversion of all ethylenic unsaturation contained in a polymer. As a result, hydrogenated polymers produced with the hydrogenation processes heretofore proposed cannot, frequently, effectively be used in polymeric compositions wherein curing is effected through crosslinking requiring ethylenic unsaturation. Moreover, such polymers cannot, effectively, be functionalized using techniques requiring residual ethylenic unsaturation. The need, then, for an improved method for hydrogenating polymeric materials containing ethylenic unsaturation which will permit the retention of a controlled amount of unsaturation in the polymer is believed to be readily apparent.